KB 2919355 is a required precursor to all future Win 8.1 updates, including security patches

The long-awaited (but not terribly well-received) and likely final suture in the Jekyll-and-Hyde version of Windows has just hit the MSDN site. For those of you who have MSDN accounts, it's time to start your downloads. For those of you without MSDN rights, in a few hours the new torrents should contain absolutely impeccable versions of the Win 8.1 Update ISO, fresh from MSDN.

If you pluck a copy from any place other than the MSDN site, make sure the file you download matches the ones on the MSDN site.

The full Windows 8.1 with Update ISO file, multiple editions (but not Enterprise), x86, U.S. English:

Filename = en_windows_8.1_with_update_x86_dvd_4065105.iso

SHA-1 = 54B8572556B316A6BECE54C5033564E3296F5951

Same thing in 64-bit:

Filename = en_windows_8.1_with_update_x64_dvd_4065090.iso

SHA-1 = 4652DC6EBFEBE02C6A63E167C36E3FAEDFB93999

The full Windows 8.1 Enterprise with Update ISO file, x86, U.S. English:

Filename = en_windows_8.1_enterprise_with_update_x86_dvd_4065185.iso

SHA-1 = FE43558B4708B4B786BC3286924813B0AAD21106

Same thing, 64-bit:

Filename = en_windows_8.1_enterprise_with_update_x64_dvd_4065178.iso

SHA-1 = 8FB332A827998F807A1346BEF55969C6519668B9

If you already have Windows 8.1 and want only the Update itself, Microsoft has kindly provided ZIP files each with six Update (MSU) files. You have to run each of the MSU files, in the sequence specified in the Readme.txt file, in order to apply the Update. (To run an MSU file in Windows 8.1, just double-click on it.)

If you download an ISO, chances are good you will be able to install a fresh copy of Windows 8.1 Update if you convert the ISO to a bootable drive, then boot and use your Windows 8.1 activation key. (There may be some fun problems with UEFI systems -- see the instructions on Eightforums for details.)

If you download one of the Update-only ZIPs and run the MSU files in the sequence specified, you'll get a full in-place "upgrade" with none of your settings changed.

In a surprising -- and not well advertised -- turn of events, Microsoft will require that you install Windows 8.1 Update before you can install any future patches. KB 2919355 states:

Important All future security and nonsecurity updates for Windows RT 8.1, Windows 8.1, and Windows Server 2012 R2 require this update to be installed. We recommend that you install this update on your Windows RT 8.1, Windows 8.1, or Windows Server 2012 R2-based computer in order to receive continued future updates.

It appears that the Windows 8.1 Update changes are in your future, whether you want them or not.

Woody Leonhard writes computer books, primarily about Windows and Office; he's currently working on the Win 10 follow-up to the thousand-page "Windows 8.1 All-in-One for Dummies." A self-described "Windows victim," Woody specializes in telling the truth about Windows in a way that won't put you to sleep.